The invention relates to a resilient bumper assembly for a vehicle having a horizontal beam, flexible sheet cladding and impact absorber of variable resilience.
Motor vehicles such as buses, trucks, tractors and passenger cars absorb the impact from collision with other vehicles or stationary objects with front and rear bumpers mounted to the vehicle frame, often with telescoping cylinders to absorb shock. In general, bumpers are expected to withstand the impact of collision at a relative velocity of 5 to 15 km/h without significant damage. Many conventional bumpers include impact absorbing means that deform permanently or resiliently during collision thus preventing damage to the vehicle frame or adjacent components. Bumper systems are generally provided in addition to other passenger restraint systems such as seatbelts and collapsible steering columns, expandable air bags that are more active on higher speed impacts.
A typical low impact absorbing bumper is shown in U.S. Pat. No. 5,139,297 to Carpenter et al. that includes a foamed energy absorbing block of polypropylene or foam that is positioned between a relatively stationary transverse beam and surrounded by a rigid forward face bar with backing bar that slide together rearwardly during impact relative to the stationary beam.
The resilient foam is contained as the face bar slides rearwardly under impact and serves to cushion the impact of collision. A disadvantage of this prior art system is that the metal components may corrode and seize up thus preventing the sliding contact between the various components upon which the entire system relies. Failure to slide and compress the foam material can cause unreliable performance and complete seizing of the sliding action can result in unexpected damage to the vehicle and injury to passengers. The rigid face bar does not itself deform locally but rather distributes the impact load more uniformly over the surface of the contained resilient component.
Another conventional bumper is shown in U.S. Pat. No. 3,888,531 to Straza et al. Rather than using a resilient shock absorbing material, Straza et al. utilizes frangible permanently deformable sheet metal formed for example in the shape of a honey comb matrix optionally filled with a wax like material to increase resistance to deformation on low impact collision. The theory behind the use of frangible shock absorbing sheet metal material is that on receiving a major impact, the frangible material will extrude the wax like material from the honeycomb cells and permanently deform the sheet metal honeycomb thereby reducing or dispersing the force of impact.
A significant disadvantage of such permanently deformable, sacrifical or frangible bumpers is apparent in the case of urban transit vehicles where frequent collisions occur with other buses during routine maintenance and rapid marshalling of the buses. The cost and inconvenience of replacing frangible shock absorbing bumpers is unacceptable and in such applications a resilient deformable bumper is preferred. However, as mentioned above in respect of Carpenter et al., corrosion, contamination with dust, and salt can detrimentally affect the sliding components of such prior art bumpers.
Various other prior art bumpers include a metal shell or plastic shell that is filled with foam shock absorbing material and mounted to the vehicle on a relatively rigid beam. Such bumpers are unsuitable for low cost fleet operations such as urban buses, trucks, delivery vehicles and taxis since frequent collisions at low impact can cause significant damage, vehicle downtime and may require replacement of the entire bumper in many cases.
It is an object of the invention to provide a resilient impact absorbing bumper that does not permanently deform during low impact collisions.
It a further object of the invention to provide an impact absorbing bumper that can be manufactured and maintained at reasonable cost and can survive collisions of low and intermediate intensity without permanent damage.
It is a further object of the invention to provide a simply constructed impact absorbing bumper that is made of modular components that can be readily removed and replaced if necessary after a major collision without significant down time.
Further objects of the invention will be apparent from review of the disclosure, drawings and description of the invention below.
The invention provides a resilient bumper assembly for a vehicle having an elongate horizontal beam mounted transversely to an end of the vehicle. Exterior flexible sheet cladding mounted on the beam defines an elongate internal chamber between its inner surface and the outer surface of the beam. An elongate resilient impact absorber is mounted to the beam and housed within the internal chamber, with top, bottom, inner and outer surfaces.
Vertically extending cavities within the impact absorber, each opening to at least one of the top and bottom surfaces of the impact absorber provide resilient collapsing and rebound of the impact absorber on impact. The absorber may include variations in the size and shape of cavities, and variations in the material of which it is moulded in order to modify the resilient characteristics of the absorber to suit different design needs. By simply adopting a different pattern, shape or size of cavity, the resilience of the absorber may be easily adjusted.
The invention provides an impact absorber, which can be adjusted or fine-tuned to suit various expected impact loadings. For example, the resilience of the impact absorber can be varied between the inner or outer surfaces or the lateral and central sections. Depending on the results of experimental testing for example, the strength of resilient plastic material of which the impact absorber is moulded can be modified or varied throughout the length, width or depth of the bumper.
In addition, the pattern, size, configuration or shape of cavities can be readily changed by merely providing different inserts in the mould that forms the impact absorber without changing the outer appearance of the bumper in any way. Therefore, a manufacturer can commit to the outer dimensions of the bumper and cladding as well as the mechanical connection of the beam to the vehicle frame while retaining flexibility in the impact absorbing properties of the bumper by modifying the size, shape, pattern and configuration of the various cavities which can be placed within the impact absorber to modify its resilient properties. Different flexibility and rebound characteristics car. be fine tuned as a result of experimental tests or as a result of observations from actual collisions in use of urban transit vehicles for example. The user need not to be committed to a particular resilience but may utilize the same outer cladding and support beam for different vehicles or different applications since the internal impact absorbing member need only be changed.
A further significant advantage of the invention is that components are manufactured in modules, which are mounted together during assembly with minimal use of mechanical fasteners. Preferably the cladding is moulded in three components which if damaged can be readily removed and replaced. The cladding is interlocked with the beam with a sliding dove tail connection and the entire bumper assembly is secured in place with minimal fasteners. In the embodiment illustrated, only four threaded studs are used to secure the entire bumper together. In contrast, many of the prior art bumpers require several mechanical fasteners and therefore include significant time and labour to manufacture and to repair after damaged in a collision. The present invention, in contrast, requires only four washers and nuts threaded onto the four threaded studs to secure all components together on the beam. In the event of damage from impact, any damaged modular components can be removed and recycled. Replacement modular components can be quickly installed on the beam thereby reducing down time for the vehicle after any collision.
In the prior art, use of a closed cell foam has the significant disadvantage that the force of impact will cause some of the closed cell air bubbles to rupture or burst when the air inside is compressed. Rupture of the walls between cells of a foam will then reduce the resistance to compression or reduce the resilient rebound of the foam mass. Repeated impacts to the foam will change the resilience of different bumpers and between different areas within the same bumper such that the overall performance of the resilient material is inconsistant and unpredictable. Use of open cell foam has the disadvantage that water is readily absorbed through leakage into the bumper, and through vapour condensation. Accumulation of water, especially in cold climates subject to freezing, also changes the resilience of the foam. Freeze-thaw cycling can cause the wet foam material Lo breakdown as the water expands and contracts repeatedly.
The present invention however provides a different means of managing the energy of impact, air flow and water accumulation. Repeated impacts do not result in changes to the resilience of the impact absorber, but rather the solid wall structure is configured such that complete recovery occurs. The cavities within the impact absorber are oriented on a vertical axis since the force of the impact of collision will be directed along a generally horizontal plane. The force of impact initially will collapse the flexible cladding. Air within the cavities can readily escape through the openings at the top and bottom of the impact absorber between the cladding and impact absorber. In contrast, closed and open cell foam absorbers of the prior art, contain air within the cells. The air in the closed cells compresses on impact since it cannot escape readily and ruptures the walls of the cells under high air pressure on impact.
In the present invention, impacts of a large magnitude will distort or collapse the vertically extending cavities within the resilient impact absorbing material. The larger the impact force, the greater the local distortion of the vertically extending cavites. The air within the cavities escapes and returns rapidly thereby allowing the impact absorber to recover it""s original shape without loss of resilience. In the case of major impacts, the modular components of the bumper may be dislodged from the beam entirely. However, reliance on the rigid metal beam prevents further damage to the vehicle even if the resilient components have been damaged or dislodged.
Further advantages of the invention will be apparent from the following detailed description and accompanying drawings.